1. Field of the Invention
The invention relates generally to integrated circuit (IC) mountings, and more particularly to an integrated circuit mounting structure having a switching power supply included therein.
2. Description of the Related Art
High-speed logic circuits contained in integrated circuit (IC) semiconductor chips typically require one or more constant DC supply voltages to be maintained at various circuit locations. In the context of IC packages mounted on a printed circuit board (PCB), these DC supply voltages are conventionally provided to the IC chip(s) by means of a central DC-to-DC power supply. The DC-to-DC power supply is typically either mounted directly on the PCB or is contained in a separate module. In the latter mounting configuration, the voltages generated by the DC-to-DC supply are conductively coupled to the PCB by means of a wire harness or connector coupled to a socket on the PCB. Then, for both prior art mounting configurations, the coupling continues through thin-film conductive tracks on the PCB to an IC package. The IC chip is coupled to the PCB either via an IC socket mounted to the PCB or directly to the external pins of an IC package. Finally, the voltages are coupled through IC package bond wires to the DC voltage-supplying bond pads of the individual semiconductor chip(s) mounted within the IC package.
In state of the art personal computers, for example, where the central processor is an increasingly more complex and higher frequency digital circuit contained on a single IC chip mounted typically on a multilayer PCB characterized as a mother board, the means for supplying DC power to this type of IC must be capable of distributing high currents while maintaining tight voltage tolerances in order for the processor chip to operate within a manufacturer""s specifications. The above-described conventional coupling of DC power to the IC chip(s) results in the drawback of relatively long power supply lines. This creates increasing difficulties in maintaining constant and regulated DC supply voltages at the IC chip(s) regardless of transient short term or average long term current demands of these chips.
One such difficulty results from variations in the voltage (or IR) drop in the conductive paths between the DC power supply and the voltage supply contacts of the IC chip(s). As the length of the voltage supply lines increases, the resistance of the lines increases. As the operating speed and complexity of circuits in an IC chip increases, with a corresponding increase in the amount of current demanded by the IC chip, variations in this current demand during normal operation of the IC chip(s) causes substantial variations in the voltage drop across the power supply lines. Normally, the voltage drop along the power supply lines can be reduced by increasing the cross-sectional area of the lines as much as possible. Unfortunately, the current demand is high enough and the constraints on mother board space significant enough that a designer may not be able to size the metal lines large enough to provide DC supply voltages adequate to guarantee proper operation of ICs that have high transient loading characteristics.
The length of the power supply conductive paths also aggravates the problem of parasitic inductive reactance between the power supply paths. Due to the high frequency operation of modern ICs, switching power supplies are subject to more and more severe transient loads. The rate of change of current required from a power supply by an IC will, due to the presence of inductance from power supply conductive paths both internal and external to the IC package, result in modulation of the power supply voltage since the current through an inductor cannot change instantaneously. This modulation of the power supply voltage, commonly referred to as power supply noise and voltage sag, can interfere with data transmission on the signal lines or otherwise interfere with IC operation, and thus pose a serious problem to optimum performance of IC circuitry. A common means of controlling the inductance problem is the use of capacitive filters or decoupling capacitors in very close proximity to an IC chip, both between the power supply terminals external to the IC package and within the cavity of the IC package. While such decoupling capacitors are effective in reducing the magnitude of the power supply noise and voltage sag at the IC chip, significant parasitic inductance still remains as a result of the length of the conductive paths between the IC chip and the power supply so that noise and voltage sag still affect the operation of the ICs.
Another drawback of the lack of physical proximity between the DC power supply and conventionally packaged IC chip structures is the time it takes for the power supply to sense the change in current demand of the ICs. Shorter path lengths between the load and the feedback circuit of a conventional power supply enable more rapid correction for the one or more output voltages generated by the power supply when the level of the output voltages is either above or below their specified level.
Prior art power supply mounting configurations are also expensive to manufacture. External connections, including power supply high current connectors and sockets, to a PCB, and the area or xe2x80x9cfoot printxe2x80x9d occupied by these components and the lengthy conductive paths on a PCB, drive up the cost of a PCB.
The above described drawbacks, ill-effects, and expense associated with conventional coupling between a DC power supply and IC chips may be greatly minimized by positioning the DC power supply as close to the IC chips as technologically possible. This is especially the case for systems where only one or a few IC chips in the system comprised the bulk of the high current demand of the system. Specifically, maximizing the conductive coupling between the power supply and such IC chip(s) will minimize the variations in voltage drop and the inductive reactance within the circuit, reduce the production of thermal build-up, and improve the responsiveness of the power supply to the variations in current demands of the IC. Moreover, more PCB area is needed by the components of the power supply. The overall packaging density can then be increased, thereby reducing the cost of packaging and substrate materials.
In accordance with the present invention, a mounting structure for providing DC power to an IC package is provided which substantially eliminates the limitations associated with prior art switching power supply structures. The present invention specifically enables a stable power supply voltage to be provided for high speed, high current demand IC chips while improving the packaging density of the system and reducing thermal dissipation.
In one embodiment according to the present invention, the mounting structure includes DC-to-DC switching power supply mounted on the IC""s socket for providing DC power to an IC package having one or more IC chips. The mounting structure includes a socket for receiving the IC package and a DC-to-DC switching power supply mounted to the socket. The DC-to-DC switching power supply is electrically coupled to the IC package by conductive paths formed in the socket for supplying at least one specified DC voltage to the IC package. The socket is mountable in a conventional fashion on a printed circuit board.
In a second embodiment according to the present invention, the mounting structure includes a DC-to-DC switching power supply mounted within a hybrid IC package. More particularly, a semiconductor packaging structure is provided which includes a hybrid IC package having at least one IC chip and a DC-to-DC switching power supply mounted within the hybrid IC package preferably on the same substrate. The DC-to-DC switching power supply is electrically coupled to the IC chip by conductive paths formed in the hybrid IC package for supplying at least one specified voltage to the at least one IC chip.
Accordingly, it is a general object of the present invention to provide a mounting structure for providing DC power to an IC package that performs better than prior art mounting structures.
It is another object of the present invention to provide a mounting structure for providing DC power to an IC package which provides close physical proximity of the DC-to-DC switching power supply to the IC semiconductor chip(s) to which it supplies voltage.
Another object of the present invention is to provide a mounting structure for providing DC power to an IC package which minimizes the voltage drop between the switching power supply and the IC semiconductor chip(s) to which it supplies voltage.
It is also an object of the present invention to provide a mounting structure for providing DC power to an IC package which reduces the inductive reactance of the conductive paths between a switching power supply and the IC semiconductor chip(s) to which it supplies voltage.
Another object of the present invention is to provide a mounting supply structure for providing DC power to an IC package which improves the responsiveness of the switching power supply to variations in the current demands of the IC semiconductor chip(s) to which it supplies voltage.
Another object of the present invention is to provide a mounting structure for providing DC power to an IC package which minimizes the amount of heat generated by the conductive coupling between the switching power supply and the IC semiconductor chip(s) to which it supplies voltage.
Another object of the present invention is to provide a mounting structure for providing DC power to an IC package in which the switching power supply is cooled by the same thermal dissipation means that is used to reduce the temperature of the IC semiconductor chip package.
Another object of the present invention is to provide a mounting structure for providing DC power to an IC package which reduces the PCB area needed by the DC power supply.
Still another object of the present invention is to provide a mounting structure for providing DC power to an IC package which is more cost effective than prior art mounting structures.
These and other objects and advantages of the present invention will become more apparent from the following detailed description and the accompanying drawings.